In extreme operating conditions such as chemical reactors, industrial furnaces, aircraft engines, and nuclear power equipment, temperature is a key parameter determining production safety and product quality. As the "temperature sensor" that directly contacts the measured medium, the thermocouple wire's temperature measurement accuracy, temperature resistance, and stability directly determine the reliability of the entire temperature measurement system. Traditional thermocouple wire has significant limitations: Common K-type (nickel-chromium-nickel-silicon) thermocouple wire is prone to nickel volatilization when used at temperatures above 800°C for a long time, resulting in a temperature drift rate exceeding ±5°C/1000h. Platinum-rhodium-based thermocouple wires (such as S-type and B-type) offer high temperature resistance (up to 1600°C), but are expensive and brittle. Cheap metal thermocouple wires are easily corroded in corrosive environments (such as acidic chemical fumes), resulting in a service life of less than three months. In recent years, breakthroughs in material formulation optimization, structural design innovation, and surface modification technology are driving the advancement of thermocouple wire toward a wide temperature range, high stability, extreme resistance, and low cost. I. Technological Breakthrough: From "Single Temperature Resistance" to "Full-Duty Adaptability"
1. Material System Innovation: Balancing Performance and Cost
We develop customized alloy systems tailored to different temperature ranges and operating conditions, addressing the "temperature resistance, cost, and stability" dilemma. Medium- and high-temperature range (600-1300°C): The N-type thermocouple wire (nickel-chromium-silicon-nickel-silicon-magnesium alloy) was launched. By adding silicon and magnesium to refine the grain size and inhibit element diffusion at high temperatures, the N-type thermocouple wire reduces the temperature drift rate to ±1.5°C/1000h at 1000°C over long-term use compared to the traditional K-type wire, improving oxidation resistance by 40%. At a cost of only 1/20 that of the S-type platinum-rhodium wire, the wire is widely used for temperature measurement in chemical reactors and ceramic kilns.
High-temperature range (1300-1800°C): Platinum-rhodium-palladium composite alloy wire (such as PtRh20Pd5) was developed to replace the traditional PtRh20Pt wire (S-type). The addition of palladium improves the alloy's toughness (elongation at break increases from 15% to 28%), preventing brittle fracture at high temperatures. This also enhances thermoelectric potential stability at 1600°C. 30%, suitable for temperature measurement in aircraft engine combustion chambers and nuclear power high-temperature steam pipelines.
Low-Temperature Range (-200-300°C): Optimized copper-constantan (T-type) thermocouple wire purity, using 99.999% high-purity copper and ultra-low carbon constantan, reduces thermoelectric potential fluctuations at low temperatures. Temperature measurement accuracy reaches ±0.3°C at -196°C (liquid nitrogen temperature). Suitable for temperature measurement in low-temperature chemical industries (such as LNG storage) and superconducting equipment.
2. Structural Design Innovation: Enhanced Resistance to Extreme Environments
This breaks away from traditional single-filament or dual-filament parallel structures, and utilizes a special molding process to enhance the thermocouple wire's vibration and bending resistance. Ultra-fine diameter and multi-twisted structure: Targeting microelectronic packaging (such as chip thermal testing) and confined spaces (such as chemical microchannel reactors), we have developed ultra-fine thermocouple wires (such as ultra-fine K-type and T-type) with diameters below 20μm. Using a "multi-pass precision drawing + inert gas annealing" process, we have increased the yield rate from 58% to 92%. We have also developed a "double-twisted structure" by spirally twisting two thermocouple wires, improving vibration resistance by 50%. For temperature measurement in engineering machinery engine cylinders, it can withstand high-frequency vibrations of 1000Hz without breaking.

Different-diameter transition structure: To meet the connection requirements between high-temperature and normal-temperature sections, we have designed a transition type thermocouple wire with a "thick diameter (high-temperature resistant) end and a thin diameter (flexible) end." The thick diameter section (such as a 1mm platinum-rhodium wire) is inserted into the high-temperature section, while the thin diameter section (such as a 0.3mm) is inserted into the low-temperature section. The nickel-chromium wire is extended to the room-temperature junction box, ensuring high-temperature stability while reducing overall installation complexity. This technology has been used for deep-hole temperature measurement in industrial furnaces.
3. Surface Modification Technology: Enhanced Corrosion and Pollution Resistance
Through coating or passivation treatment, a "protective barrier" is created for the thermocouple wire, making it suitable for harsh environments such as chemical corrosion and high dust levels. High-temperature oxidation-resistant coating: A plasma-sprayed Al₂O₃-ZrO₂ composite coating (5-10μm thick) is applied to the surface of N-type and S-type thermocouple wires. This coating reduces the oxidation rate by 70% in sulfur-containing flue gas at 1200°C, extending its service life from 3 months to 18 months. It is used for temperature measurement in sulfur incinerators in chemical sulfuric acid production plants.
Corrosion-resistant passivation: Chemical passivation (e.g., chromate passivation) is applied to copper-constantan and nickel-chromium-copper-nickel (E-type) thermocouple wires. The corrosion rate in 5% hydrochloric acid solution is reduced from 0.2mm/year to 0.03mm/year, making it suitable for temperature monitoring of chemical acid and alkali storage tanks.
Anti-coking coating: A modified polytetrafluoroethylene (PTFE) coating is applied to the surface of thermocouple wires used in coal chemical gasifiers to prevent coal tar adhesion, reduce temperature measurement deviations caused by coking, and extend the cleaning cycle from one week to one month. II. Implementation: Covering Applications from "Civil Industry" to "High-end Equipment"
1. Chemical Industry: Overcoming the Dual Challenges of Corrosion and High Temperature
In applications such as coal chemical and petrochemical industries, thermocouple wires must withstand both high temperatures and corrosive media. A coal-to-olefins company uses an "N-type thermocouple wire + Al₂O₃ coating" combination for temperature measurement in gasifiers (1200°C, containing H₂S and CO₂). Compared to traditional K-type wires, this extends the service life from 2 months to 15 months, and maintains a temperature measurement deviation within ±2°C, preventing fluctuations in gasification efficiency caused by temperature misjudgment. In fine chemical batch reactors (300-500°C, containing organic acids), passivated E-type thermocouple wires are used to monitor reaction temperatures in real time, ensuring the selectivity of synthesis reactions (for example, increasing the conversion rate of ester synthesis by 5%). 2. Aerospace: Withstanding Extreme Temperature Differences and Vibration
Aircraft engine combustion chamber temperatures can reach as high as 1600°C, accompanied by high-frequency vibrations. Traditional S-type platinum-rhodium wires are prone to brittle fracture. One aviation company uses PtRh20Pd5 composite alloy wire, combined with a twisted structure. During engine testing, this wire can stably measure temperatures at 1600°C for 500 hours, with thermoelectric potential fluctuations of ≤±0.5% under vibration conditions, providing precise temperature data for engine thrust optimization. In spacecraft thermal control systems, ultra-fine T-type thermocouple wire (25μm diameter) is used to monitor the temperature distribution of satellite solar panels. Its measurement accuracy reaches ±0.2°C, adapting to the extreme temperature differences of -180°C to 100°C in space.
3. Nuclear Power: Ensuring Long-Term Stability and Safety
Nuclear power primary circuit piping (temperatures of 320°C, high-pressure boron-containing water) places stringent demands on the corrosion resistance and long-term stability of the thermocouple wire. A domestic nuclear power project uses a combination of Hastelloy C-276 alloy sheath and N-type thermocouple wire. Hastelloy alloy offers excellent resistance to intergranular corrosion. After five years of use in boron-containing water, the thermoelectric potential drift of the thermocouple wire is only ±0.8°C/1000h, meeting the safety requirement of a 60-year design life for nuclear power equipment.

III. Future Trends: Towards "Intelligent Sensing + Green Circulation"
Currently, the domestic thermocouple wire industry has transitioned from "mid- and low-end import substitution" to "high-end technological breakthroughs." By 2024, the domestic thermocouple wire market is projected to exceed 5 billion yuan, with a domestic production rate of 85% for N-type and ultra-fine thermocouple wire. Platinum-rhodium-palladium composite wire boasts performance comparable to international brands. Future technology upgrades will focus on two key areas:

Intelligent Integration: Integrating thermocouple wires with microsensors (such as vibration and pressure sensors) to develop integrated "temperature-multi-parameter" sensing wires. These can simultaneously monitor the temperature and pressure of chemical reactors, with data wirelessly transmitted to the control system for predictive maintenance.

Green Recycling: Developing a "high-temperature dissolution-selective extraction" recovery process for precious metal thermocouple wires such as platinum and rhodium, achieving a precious metal recovery rate of 99.5% and reducing raw material costs. For inexpensive metal thermocouple wires, biodegradable coatings will be applied to reduce environmental pollution after disposal.

As the "temperature nerve" of thermocouple wires under extreme operating conditions, technological upgrades to thermocouple wires not only support safe and efficient operation in the chemical, aviation, and nuclear power industries, but will also become a key foundational component of the "sensing layer" of the Industrial Internet, providing core material support for intelligent manufacturing and the localization of high-end equipment.